Non-Pitched Atmospheric Sounds

Non-pitched atmospheric sounds are used in film making to create a similar feeling to what the score tries to establish, but in a more subtle fashion. They aren't usually very noticable unless you're looking for them, but will still have the effect regardless of if you're aware of a sound being played.

A brilliant example of the effectiveness of atmospheric sounds is Orin Peli's "Paranormal Activity". Often throughout the film, when there is a silence, an extremely low rumble is used to create subtle suspense and a feeling of uneasiness in the viewer.

Note how the extremely low frequency sound stops as soon as the door slams shut. The sound is used to build suspense, to make the viewer aware that something is going to happen. This is very effective on high end sound systems such as those in cinemas where the subwoofers can produce extremely low sounds. Found footage movies like this generally have no score or non-diegetic sounds, so these techniques are usually relied on to keep it subtle and make it feel more realistic than high-budget blockbuster.

Another great use of non-pitched sounds is found in Darren Aronofsky's "Requiem for a Dream". This scene depicts two friends who are in a prison cell and one of them has an extremely infected arm due to heroin abuse.

The sounds in this scene seem to be some kind of highly distorted screeching, and are used in direct conjuction with the video (heavily shaking image) to create the feeling of overwhelming desperation among the two characters. Notice how the sounds get louder and the image shakes more violently as the characters get louder and more desperate for help.

My third and final example is from Danny Boyle's "127 Hours" which is a true story of a man named Aron Ralston who is trapped in a narrow canyon due a small boulder being wedged on his arm. After spending around five days in the canyon, he decides that he must amputate his arm in order to be freed, which is recreated in this scene.

The most obvious and effective sounds in this particular scene are the stinging screech sounds which are heard whenever he touches the nerve in his arm. These give us a feeling of something that is extremely unpleasant, and the noise is akin to that of nails on a blackboard which is known to make a person cringe, much like the thought of doing what he is doing to himself in this scene.